1. Technical Field
The present disclosure relates to calibration involving calculating a camera installation parameter on the basis of an image photographed by a camera.
2. Description of the Related Art
A technique for measuring the distance between a vehicle and an object in front of or behind the vehicle using a camera installed at the vehicle to issue a warning to a driver has been prevalent in recent years. To accurately measure the distance between the vehicle and the object, it is desirable to accurately calculate an installation location and an installation angle of the camera with respect to the vehicle (perform calibration).
Common calibration techniques for obtaining an installation angle of a camera with respect to a vehicle include a technique utilizing a point (vanishing point) where parallel straight lines in a real space intersect in an image space.
The calibration technique utilizing a vanishing point calculates a camera installation angle from at least two vanishing points, a vanishing point (depth vanishing point) calculated from parallel lines parallel to a traveling direction of the vehicle and a vanishing point calculated from any other parallel lines.
A camera installation angle will be referred to as a camera installation parameter hereinafter.
Calibration techniques for calculating a camera installation parameter utilizing a vanishing point include a technique for extracting two sets of parallel lines in a real space from a photographed image of a road marking, graphic feature quantities of which are stored in advance, to calculate two vanishing points from the extracted two sets of parallel lines (Japanese Unexamined Patent Application Publication No. 2008-11174).